For reasons of efficiency, steam is increasingly being used as coolant for cooling components of energy machines, for example of a gas turbine installation, which are subject to high thermal loads. This steam can flow through the components which are to be cooled in an open, semi-open or closed system either in the form of steam or in the form of a steam/air mixture.
In an open steam system, the steam is guided from a device for providing steam (heat recovery steam generator, steam turbine installation, auxiliary steam generator, etc.) to the device for using steam, for example a gas turbine installation, in order to cool the components of this device which are heated. The cooling steam, after it has flowed through the cooling system of the gas turbine installation, for example, passes into the working medium of the gas turbine installation and ultimately into the atmosphere together with this medium.
In a semi-open steam system, the steam is guided from a device for providing steam (heat recovery steam generator, steam turbine installation, auxiliary steam generator, etc.) to the device for using steam, for example a gas turbine installation, in order to cool the components of this device which are heated. After it has flowed through the cooling system of the gas turbine installation, the cooling steam is fed to a device for removing steam (heat recovery steam generator, steam turbine installation, technological process, etc.).
In a closed steam system, the device for providing steam (steam cooler, steam blower, steam filter, etc.) is identical to the device for removing steam. Steam with the appropriate parameters is made available to the device for using steam, in this case the gas turbine installation, by the device for providing steam. After it has flowed through the cooling system of the gas turbine installation, the steam is returned to the device for providing steam, in order for the increase in pressure, cooling, cleaning and the like required to maintain the cycle to be carried out.
The various steam systems have been explained with reference to the example of a steam system for cooling gas turbine installations. Although the main function of the steam in this example relates to the cooling of components, during which process the steam is heated, there are also areas within such a system, for example pipelines or fittings, in which the steam is cooled. The steam systems may to a certain extent also be heating systems based on steam. Therefore, the steam systems include both cooling systems, in which the steam is heated, and heating systems, in which the steam is cooled.
In the case of steam injection for increasing power, steam is injected as an additional working medium in order to increase the mass flow of working medium into the gas turbine installation. This may in turn take place in the form of direct injection of steam into the working medium or indirectly after it has flowed through gas turbine components which are to be cooled. However, the steam may also be injected into the working medium indirectly, i.e. after it has flowed through gas turbine components which are to be cooled, in the form of a steam/air mixture, i.e. in combination with cooling air via an open air cooling system.
The steam injection method, i.e. the introduction of steam into the working medium of the gas turbine installation, is also used in the Cheng cycle. In the Cheng cycle, to avoid a steam turbine installation and the systems required for operation of the steam turbine installation, the steam which is generated in the heat recovery steam generator is injected in its entirety into the gas turbine installation.
Contaminants originating from steam-soluble substances in steam which is guided in this manner may lead to deposits forming on components around which the steam flows and therefore cause problems. From the wide range of possible contaminants, the silicates are of particular importance with regard to possible deposits, on account of the problems involved in cleaning make-up water and condensate and the frequent contamination during installation and maintenance work. Therefore, silicates are mentioned as a representative example of the wide range of possible contaminants.
The high-precision components of a gas turbine installation, the small dimensions of the cooling passages, the high demands imposed on the flow conditions and the like result in the need to ensure a high quality of steam. Without this purity, deposits are formed within the steam systems, the performance of the installations is reduced and maintenance work, with corresponding installation shutdown times, become necessary. This is of importance in particular for open and semi-open systems, since in these systems the cooling steam constantly has to be provided as new, and therefore it is always possible for new contaminants to enter the system.
This results, not least, in numerous constraints being imposed on the steam generator technology used, for example with regard to component design (steam drying in drums and separators), the temperature control for the steam by injection of water or mixing of steam, chemical procedures, etc.
It is currently attempted, for steam systems of this type, to ensure a high quality of steam which avoids deposits with considerable reliability, by suitably designing the feed water preparation and the steam generation. For example, numerous steam-mixing methods are known allowing the steam temperature to be controlled without the injection of water. Furthermore, special steam filters, in particular for closed steam systems, are recommended.
For steam applications of this nature, with disadvantageously high technical and therefore also financial outlay, all these approaches are based, for example, on ensuring that very pure make-up water is generated, on ensuring a high level of purity of the feed water in water/steam cycles by means of condensate-cleaning installations, on avoiding contamination to the steam by using suitable processes for generating the steam and controlling its parameters, on removing contaminants from the steam by means of suitable filters, and on preventing chemical interactions, for example corrosion, in the corresponding systems by means of a suitable choice of materials. These measures are used both individually and in combination.
A drawback of these possibilities is that, for example, it is no longer possible to use tried-and-tested chemical procedures for steam generators. Moreover, condensate-cleaning installations, in addition to a high outlay in terms of investment and operating costs, also entail additional risks. Steam filters for separating out particles which are entrained in the steam also only have a limited effect.
Alternatively, however, the prior art, when it is restricted to the field of steam generation or evaporation, i.e. the transfer of water from the liquid state into the vapor state, proposes metering various additives, especially amines, into the feed water, in order, in this limited field, to limit the formation of deposits or to partially eliminate deposits which are already present. For example, U.S. Pat. No. 4,476,930 and U.S. Pat. No. 6,017,399 describe possible ways of limiting deposits in evaporator systems by means of additives, including in combination with a reduction in the levels of corrosion.